The present invention relates to energy storage devices, and more specifically, to field effect transistor (FET) capacitors.
In silicon on insulator (SOI) technologies, creating a decoupling FET capacitor is a known process. Typically, creating a decoupling FET capacitor includes creating source and drain regions adjacent a channel. The source and drain are both typically doped in the same manner. For example, both the source and drain could be N+ doped or both are P+ doped. Such doping works fine for a unidirectional capacitor.
Building a capacitor, however, that would work in both bias directions is not straightforward. Such a capacitor would need to be able to store charge regardless of whether Vdd or a reference voltage (ground) is applied to the gate of the de-coupling capacitor. For a capacitor to work in accumulation mode in SOI, a body tie is required, and this would normally have problems with parasitic resistances and capacitances that would limit the operation.